1. Field of the Invention
The present invention relates generally to optical fiber devices and methods, and in particular to an improved cascaded Raman lasing system.
2. Background Art
Raman lasing systems are useful devices for converting laser light at a first wavelength into laser light at a second, longer wavelength. One important use for Raman lasers is to provide wavelength conversion for rare-earth fiber lasers. A typical ytterbium (Yb) fiber laser, for example, may emit light at 1117 nm. Infrared optical communications, however, commonly operate in the C-band, i.e., 1530 nm-1565 nm, which corresponds to the amplification range of an erbium-doped fiber amplifier (EDFA). Thus, a Raman laser can be used to convert a Yb-laser emission having a wavelength of 1117 nm into a high-brightness laser light having a wavelength of 1480 nm that can be used to pump an EDFA operating in the C-band.
For a number of reasons, Raman lasing technology has not yet reached its full potential in the industry. One significant issue that must be addressed is efficiency. Even the most sophisticated Raman lasers in the prior art have been unable to achieve a conversion ratio of greater than 50%.
Such lasers are fabricated, such as n conjunction One use for a Raman laser generating laser outputs at wavelengths at which rare-earth ionic gain is not available, e.g., near-infrared (NIR) wavelengths. A Raman laser provides a stepwise transition from a starting wavelength to a selected target wavelength. The stepwise transition is created through cascaded lasing of one or more Raman orders in a suitable Raman gain medium.
One way to bring about cascaded lasing in a Raman gain medium is to provide a set of input gratings at a first end of the Raman gain medium and a corresponding set of output gratings at a second end of the Raman gain medium. Individual input gratings are wavelength-matched to individual output gratings so as to create a nested series of in-line grating pairs. The grating pairs define a nested series of Raman cavities in the Raman gain medium.